1. Field
The present invention relates to an image pickup apparatus including a digital camera, an image data recording medium for recording image data that are output from the image pickup apparatus, and an image processing apparatus for executing processes including displaying and printing of image data, as well as an image recording program and an image processing program for executing an image data processing.
2. Description of the Related Art
An image pickup apparatus such as a digital camera generates image data representing the colors of pixels by carrying out an interpolating process for electric signals that correspond to R, G, B components obtained in an image pickup device, taking into consideration the characteristics of the image pickup device, the characteristics of the filters, and the characteristics of the display device. After undergoing an encoding process according to the JPEG format or the like, the image data are recorded into a recording medium such as a memory card.
In the process of this encoding, the image data including R, G, B signals obtained by the interpolating process are encoded after they have been converted into a signal system that is compatible with an encoding process (for example, Y, Cb, Cr signals). On the other hand, when reproducing the encoded image data and displaying the image through a display device, the just-mentioned Y, Cb, Cr signals are again converted into R, G, B signals.
The conversion process in this picture reproduction is executed according to the sRGB standard concerning the characteristics of a standard display, which is specified by IEC (International Electrotechnical Commission), assuming that the image is reproduced by a display that conforms to the sRGB standard.
The color gamut specified by the sRGB standard, however, does not cover the entire human visible region, so there exist colors that are within the human visible region but are not contained in the color gamut specified by the sRGB standard. Since such colors cannot be expressed by the image data that conform to the sRGB standard, such colors are approximated by colors within the color gamut specified by the sRGB standard.
In order to avoid such a limitation of the color gamut of the sRGB standard, a technique has been developed that enables a wider color gamut to be reproduced by adding a color profile in which wider color gamut characteristics are described as display characteristics to the image data and carrying out the conversion into R, G, B signals based on this color profile.
On the other hand, the scRGB standard, which is an extended version of the sRGB standard, is also specified by the IEC (see the non-patent reference 1). The color gamut of the scRGB standard covers the human visible region entirely, but at the same time, it can also define the outside of the visible region, in other words, the points in the range in which humans do not recognize as “colors.”
[Non-patent Reference 1] INTERNATIONAL STANDARD IEC 61966-2-2
The above-mentioned method in which a color profile is added to image data enables the entire visible region to be represented by combinations of R, G, B components by setting the points corresponding to the chromaticities of primary colors (R, G, B) which represent color gamut characteristics to be outside the visible region. At the same time, however, it allows the points outside the visible region to be defined also as “colors,” as in the case of the scRGB standard.
For such “colors” that are defined outside the visible region, no clear guideline has yet been presented as to how they should be handled in the process of outputting them through a display device or a printer. For this reason, there is a risk that some confusion may be caused in the processing stage of the image data when the image data is represented by whichever method.
In either of the cases, a value range that can be defined but is not utilized as effective data representing actual colors is produced because a data region is allocated to a region outside the visible region as well as the inside of the visible region.